1. Field of the Invention
The present invention relates generally to devices used for removing fasteners and, more particularly, to a device for removing one way fasteners having flat portions and convex portions located generally in diametrically opposite quadrants.
2. Background of the Invention
One way fasteners are well known. Generally, these fasteners are constructed with features that allow a threaded shank portion of the fastener, usually a threaded screw type configuration, to pass through an orifice in one structure and ultimately "screw" into an adjacently positioned second structure until a head portion of the fastener engages the first structure. Once the head portion engages the first structure, the one way fastener is very difficult to remove due to diametrically opposed flat and convex portions that are configured to provide a recess that receives a screwdriver and allows the screwdriver to forcibly insert the fastener into the second structure when the screwdriver is rotated clockwise, but prevents the screwdriver from extracting the fastener when the screwdriver is rotated in a counter-clockwise direction.
Conventional one way fasteners are nothing more than a conventional rounded head screw with diametrically opposed quadrants machined flat. This rounded head feature contributes significantly to the problem of extracting a one way fastener. One way fasteners are very effective in preventing unauthorized persons or vandals from separating the fastener-joined structures. However, occasions do arise requiring the difficult task of removing one way fasteners.
Prior art extraction devices utilize features such as jaws to grasp the sides of the head of a fastener for removal. Examples of such devices are illustrated in U.S. Pat. Nos. 5,551,320 and 5,533,426. Unfortunately, these devices are of no use when there are no accessible sides to the fastener head.
Another prior art extraction device details a tool having a pair of "tips" for engaging a pair of tip receiving recesses in the head of the one way fastener. Such a device is depicted in U.S. Pat. No. 5,450,776 issued to the applicant. The device further includes a collar with asymmetrical radial serrations to grasp the periphery of the fastener head. This tip-recess and collar-head interaction provides the "foothold" necessary to maximize the effect of any rotational force applied to the fastener removal tool. This device is limited to extracting a specially designed fastener. The device cannot function optimally when a conventional fastener such as that described above is encountered.
A need exists in the art for an inexpensive, quick set-up fastener removal tool for extracting one way fasteners having heads with flat portions and rounded or convex portions positioned in diametrically opposite quadrants. The removal tool should also facilitate extraction in situations where the fastener is counter sunk.